1. Field of the Invention
The invention relates to a method for manufacturing components from light metal strip.
2. Description of the Prior Art
In a light metal strips of naturally hard Al alloys, in particular of the AlMg or AlMg--Mn types, problems occur during cold forming at the cut edges from slitting, attributable not only to the microcracks caused by the slitting but also in particular to the cold hardening brought about as a result. To ensure greatest possible plasticity, the entire sheet bars are soft-annealed in the stack or the entire coil is soft-annealed in a so-called bell-type furnace. During drawing off of the strip from the soft-annealed coil, the coil curvature is straightened until flat. This straightening produces a certain additional cold hardening, which leads to a further increase in the yield strength and reduction in stress. What is disadvantageous in the known methods is the amount of energy and time expended for the soft-annealing of the entire material.
DE 3247698 C2 discloses an intermediate annealing of strip of an AlMgMn alloy. This intermediate annealing, which takes place between two successive cold rolling passes, is carried out as coil annealing at a temperature of 300 to 410.degree. C. during a period of 1/2 to 8 hours. Alternatively, the annealing may also take place at 300 to 400.degree. C. as continuous strip annealing for a period of 2 seconds to 2 minutes. Both annealing methods expend considerable amounts of energy (time, temperature) and the handling effort is also considerable. The last-mentioned annealing method for continuous strip annealing also requires enormous expenditure on equipment.
DE 4313543 C1 discloses a method for the heat treatment of continuous light-metal strips. For thin-walled strips with a thickness of 0.02 to 1.5 mm in particular, problems occur in the edge region in cases of high through-running speeds and/or great strip widths. The edge regions often become wavy, which may disrupt later processing. This edge region effect can be avoided if more heat is supplied per unit area to the edge regions of the strip than to the central region of the strip, at least over part of the treatment zone. This type of annealing corresponds in principle to continuous strip annealing with a steeper temperature gradient in the edge region to avoid wave formation. The already known disadvantages of continuous strip annealing likewise apply here.